Field of the Invention
This disclosure relates to an image forming apparatus such as a copier, a printer, a facsimile, or multi-function printer having a plurality of functions, in which an electro-photographic system or an electrostatic recording system is used.
Description of the Related Art
Hitherto, in an image forming apparatus configured to form an image by a toner such as an electro-photographic type image forming apparatus, a two-component developing system using a two-component developer that is composed of mainly mixing the toner and a carrier is widely used. In the image forming apparatus, the two-component developer is borne onto a developing sleeve which is a developer bearing member, and the toner in the two-component developer is supplied to a photosensitive drum which is an image bearing member. A surface of the photosensitive drum is charged to a predetermined charge potential, and an electrostatic latent image is formed by exposing the surface. In addition, by applying a predetermined development voltage to the developing sleeve, the toner which is charged to the same polarity as charge polarity of the photosensitive drum is adhered to the electrostatic latent image, and a toner image is formed.
Here, it is desirable that a difference (Vback) between a potential (Vd) on the photosensitive drum of a non-image portion in which the electrostatic latent image is not formed, and a value (Vdc) of a DC component of the development voltage applied to the developing sleeve, is controlled to be within a predetermined range. That is, “carrier adhesion” occurs in which the carrier in the two-component developer borne on the developing sleeve is adhered to the photosensitive drum when Vback is large, and on the contrary, a so-called “fogging” occurs in which the toner is adhered to the non-image portion of the photosensitive drum when Vback is small. In particular, since there is a possibility that the surface of the photosensitive drum is damaged when the carrier adhesion occurs, in the related art, Vback is controlled to suppress the occurrence of the carrier adhesion.
It is desirable that the relationship of Vback is maintained when the voltage falls when application of each voltage is stopped in response to completion of image formation, and when the voltage rises when application of each voltage is started in response to start of the image formation. In particular, in the case where the voltage falls, in order to reduce the carrier adhesion to the photosensitive drum, a development voltage and a charge voltage fall after rotation of the developing sleeve is stopped. Here, after the rotation of the developing sleeve is stopped, when Vback is applied between the developing sleeve and the photosensitive drum, there is a case where a phenomenon occurs in which the toner in the developer on the developing sleeve is adhered to the developing sleeve due to the influence of an electric field. When the toner adhesion to the developing sleeve occurs, a belt-like image (abnormal image) is generated at a sleeve pitch in the next output image. Therefore, JP-A-2010-134205 suggests controlling Vback in order to reduce the toner adhesion to the developing sleeve.